We intend to pursue the detailed biochemical and physiological study of mutants defective in the adenylylation system for GS. In particular we shall use genetic methods to separate the suppressor mutations from the suppressed glnB mutation to understand clearly the role of these mutations in the regulation of GS synthesis. In S. cerevisiae we shall attempt to isolate mutants in which the formation of the proline-degrading enzymes is insensitive to ammonia. We shall make use for this purpose of the observation that methylamine mimics ammonia in this regard, and thus inhibits growth on glucose-proline. Mutants resistant to methyl-amine will be isolated and examined for the specificity of the resistance. We hope in this manner to investigate the relation between induction and ammonia repression.